First Gmat, now GRE?

Well, I don't think you have to worry about quant, because GRE math is waaaaaaaay easier than GMAT math. (This is coming from someone who is terrible at math, so if I found the GRE math more manageable, it should be a breeze for you!)

I've only recently begun prep and have taken a couple practice tests, and the thing that jumps out at me as being the most difficult would be the sentence completion. Some questions require you to add 3 words to a sentence to complete it, and you only get credit if you get all 3 words right. There are words I have never seen, and being a native speaker and an avid reader, I was surprised at all the words I did not know. So I think that would be the biggest challenge. I think the materials you have will be sufficient...I hear the Barron's vocab lists are particularly helpful.

There is a thread with free practice tests in it (a couple topics down from this one), so I would recommend you maybe take one to see where you're at and go from there.

Good luck!